MM-25095: Handles static JS and CSS using Brotli encoding. (#14524)

* MM-25095: Handles static JS and CSS files using Brotli.

* MM-25095: Linting fix.

* MM-25095: Adds missing license.

* MM-25095: Moves initialization of slice.

* MM-25095: Moves initialization of slice.

api4/handlers.go

@@ -6,8 +6,8 @@ package api4
 import (
 	"net/http"
 
-	"github.com/NYTimes/gziphandler"
 	"github.com/mattermost/mattermost-server/v5/web"
+	"github.com/mkraft/gziphandler"
 )
 
 type Context = web.Context